What is the most difficult tsumego-like problem ever composed ? For a long time, I thought it was this one, from the old Chinese classical book Xuan Xuan Qi Jing, and nicknamed by our French master "the emperor of life and death problems":
But in fact, after the discovery of new copies of the Igo Hatsuyoron in the 1980's, it is widely believed that this is
"the most difficult problem ever" (if you don't speak French, the problem is "Black to play and win the game"; as the solution is more than 170 moves long, this may immediately give you an idea of the incredible difficulty of the thing).
Composed by Dosetsu himself, it is (in the words
of Fujisawa Shuko, who solved it with the assistance of some of his students) "a lifetime masterpiece, with elegant shapes, a striking novelty of the theme, a precise balance of the fights, etc."
You will find there a
solution too (alas, in French, and a lot of commentaries are necessary, for example to understand why on earth the winning maneuvre for Black is to put his own 20 stones in atari, and why White won't capture . . .).
Bob McGuigan: In another amazing whole-board problem, composed by Dosaku or perhaps Dosetsu, Black captures 72 stones but is unable to make a living group. I don't know of an online source but it is given as problem 20 in Nakayama Noriyuki's Treasure Chest Enigma.
f3etoiles It is online, on the site of goproblems.com, and Nakayama attributed it to Dosaku (but he may be a little bit biased in his judgment :-)) While we are on it, the same site has also the
Dosetsu problem (with a Java solution, but I believe there are some mistakes in it, and it doesn't show the 1 point victory), and another incredible full-board thing, called
No Man's Land.